Seen as the bible for future development in San Francisco, the Planning Commission is set to take up an oft-delayed master plan for housing that calls for a little more density in western San Francisco and for the community to become more involved in the planning process.

The plan, which is more a policy guide than a binding plan for development, has been two years in the making. If it is approved today, it would renew San Francisco's commitment to build new affordable housing near transit while still preserving the low-density character of many neighborhoods.

That balance has frustrated both sides. Housing advocates say the plan doesn't do enough to address San Francisco's critical shortage of cheap housing, while neighborhood preservationists say replacing homes with apartments will ruin San Francisco.

"It is sort of like urbanists versus the NIMBYs, not to characterize it too broadly," said Tim Colen, head of San Francisco's Housing Action Coalition, a proponent of high-density development.

State law requires that the city revise its housing master plan - commonly called the housing element - every five years to reflect projections for growth and environmental goals.

This time, San Francisco is tasked with finding room for 31,000 new units that are projected to be needed over the next seven years, said Kearstin Dischinger, a city planner.

And because most land in San Francisco is already accounted for, that means allowing some buildings - especially those near Muni or BART - to become taller or house more people.

But many residents of the city's Richmond and Sunset districts worry they'll lose their yard, their parking spot or the breathing room afforded by low-rise housing.

"Most people love the neighborhood they live in, and that's why they live there," said Hiroshi Fukuda, with the Coalition for San Francisco Neighborhoods. "It could become another Manhattan if you just have one large apartment building after another - and that's not what people love about San Francisco."

The city should slow down and further study the impact of its proposed changes, he said.

"If you're talking about allowing increased density along bus lines - that's all over the city," he said.